Influence of Equal-Channel Angular Pressing on Changes in the Microstructure of Steel Grade 1055

This work discusses the relationship between the initial structural state of steel 1055 and the evolution of its microstructural and mechanical properties under the influence of equal-channel angular pressing (ECAP) in a stepped matrix. Deformation was performed at a temperature of 400°С along the Bc route with the billet turning 90° around the longitudinal axis for six passes. It was shown that the effect of the initial structure (ferrite-pearlite, martensitic, troostite) on the structural state and mechanical properties of ultrafine-grained steels consists in the inheritance of the original grain structure and mechanical properties during ECAP. It was also revealed that after six ECAP passes, regardless of the initial structural state, a relatively homogeneous grain structure with a grain size of 0.7–1.2 μm is formed, providing high mechanical property values. The highest strength characteristics were obtained in samples with an initial martensitic structure. Thus, the ultimate tensile strength and conventional yield strength increased from 1510 to 1843 MPa (an absolute increase of 333 MPa) and from 1315 to 1691 MPa (an absolute increase of 376 MPa), respectively; the relative elongation decreased from 11 to 4%, while the relative narrowing decreased from 35 to 11%.